The present invention relates generally to series hybrid transmission and to gear-shifting methods for series hybrid transmissions.
Typical truck transmissions have between six and twelve gear ratios, and use an idler gear to drive the truck in a single reverse gear. Truck engines ordinarily operate at speeds of about 2100 rpm.
Series hybrid transmissions connect an engine to a generator which, in turn, provides power to an electric motor that can drive a shaft of a transmission. The motors can often operate at much higher speeds than the engine, such as around 4500 rpm. Power that is not used by the motor can be stored in a storage device such as a battery. The transmission will often also be arranged to provide for regenerative braking.
In a typical series hybrid transmission, a single motor drives a shaft with a plurality of drive gears that are rotatably but not axially movably mounted on and the shaft and that are individually be engaged by a clutch that is non-rotatably but axially movably mounted on the shaft. To shift between gears, a clutch engaging one drive gear must first disengage before a clutch for engaging a higher or lower drive gear can engage, which interrupts torque transmission during shifting. This can be particularly disadvantageous when an increased load is imposed, such as when changing from traveling along a flat road to traveling uphill, and it is necessary to downshift to a lower gear. Additionally, the downshift will ordinarily result in a loss of vehicle speed.
It is desirable to provide a transmission that provides a multi-speed reverse. It is desirable that such a transmission be of minimal complexity. It is further desirable to reduce, minimize, or eliminate torque interruption during shifts.
According to an aspect of the present invention, a series hybrid transmission comprises a first motor device for driving a first shaft, a second motor device for driving a second shaft, a first drive gear rotatably but not axially movably mounted on and the first shaft, a second drive gear rotatably but not axially movably mounted on the second shaft, a first clutch non-rotatably but axially movably mounted on the first shaft, the first clutch being movable to a first position in which it engages with the first drive gear to cause the first drive gear to rotate with the first shaft and to a second position in which it disengages with the first drive gear, a second clutch non-rotatably but axially movably mounted on the second shaft, the second clutch being movable to a first position in which it engages with the second drive gear to cause the second drive gear to rotate with the second shaft and to a second position in which it disengages with the second drive gear, an output shaft comprising a first driven gear non-rotatably mounted on the output shaft and in engagement with the first drive gear and a second driven gear non-rotatably mounted on the output shaft and in engagement with the second drive gear, and a controller for controlling movement of the first clutch and the second clutch, while also controlling application of torque to the first shaft and the second shaft by the first motor device and the second motor device, respectively, from a first configuration in which the first clutch is engaged with the first drive gear and the second clutch is engaged with the second drive gear to a second configuration in which the first clutch is disengaged from the first drive gear and the second clutch is engaged with the second drive gear.
According to another aspect of the present invention, a gear-shifting method in a series hybrid transmission is provided, the series hybrid transmission comprising a first motor device for driving a first shaft, a second motor device for driving a second shaft, a first drive gear rotatably but not axially movably mounted on and the first shaft, a second drive gear rotatably but not axially movably mounted on the second shaft, a first clutch non-rotatably but axially movably mounted on the first shaft, the first clutch being movable to a first position in which it engages with the first drive gear to cause the first drive gear to rotate with the first shaft and to a second position in which it disengages with the first drive gear, a second clutch non-rotatably but axially movably mounted on the second shaft, the second clutch being movable to a first position in which it engages with the second drive gear to cause the second drive gear to rotate with the second shaft and to a second position in which it disengages with the second drive gear, and an output shaft comprising a first driven gear non-rotatably mounted on the output shaft and in engagement with the first drive gear and a second driven gear non-rotatably mounted on the output shaft and in engagement with the second drive gear. The method comprises controlling application of torque to the first shaft and the second shaft by the first motor device and the second motor device, respectively, and controlling movement of the first clutch and the second clutch, while also controlling application of torque to the first shaft and the second shaft by the first motor device and the second motor device, respectively, from a first configuration in which the first clutch is engaged with the first drive gear and the second clutch is engaged with the second drive gear to a second configuration in which the first clutch is disengaged from the first drive gear and the second clutch is engaged with the second drive gear.